Title

Authors

Date of this Version

2007

Comments

Published by U.S. Department of the Interior (2007) 29 pp.

Abstract

Landscape patterns of broadleaved noxious weeds across the Cascade-Siskiyou National Monument are examined in the context of environmental and management factors to improve our understanding of weed dynamics. Environmental factors include a range of topographic edaphic variables, while management factors provide insight about historic vegetation manipulation, road construction and forage utilization by wildlife and livestock. Distribution patterns of Canada thistle (Cirsium arvense) and yellow starthistle (Centaurea solstitialis) across the Monument are best described by a combination of topographic, edaphic, biotic, and management factors. Variables incorporated within models describing landscape patterns of weeds varied with response variable (actual weed locations versus weed density at random locations throughout the landscape) and the incorporation of private lands, characterized by less intense or localized lack of weed surveys, with public lands. Optimization of data quality by restriction of analysis to public lands in a landscape context identified elevation, maximum forage utilization by livestock and native ungulates, and past management treatments as predictors common to both Canada thistle and yellow starthistle distribution. Additional variables associated with the pattern of Canada thistle included heat-load and soil depth. The optimal model describing yellow starthistle distribution also included soil classification as vertisol, NRCS ecological type, woody vegetation cover, and average utilization by livestock and native ungulates. Analysis of individual variables indicated that roads and distance from water influenced the distribution of weeds. The association between roads, water, and forage utilization implies a synergy between road construction, proximity to water, livestock and wildlife dispersion, with weed establishment.